State Water Resources Research Institute Program

Project ID: 2009WI216B
Title: Combination of Co-Precipitation with Zeolite Filtration to Remove Arsenic from Contaminated Water
Project Type: Research
Start Date: 3/01/2009
End Date: 2/28/2010
Congressional District: 1
Focus Categories: Toxic Substances, Treatment, Groundwater
Keywords: arsenic, drinking water, filtration, metal cations, Wisconsin
Principal Investigator: Li, Zhaohui
Federal Funds: $ 10,954
Non-Federal Matching Funds: $ 3,333
Abstract: Groundwater containing arsenic contamination imposes a great threat to people worldwide as well as to the residents of the state of Wisconsin. With the enactment of USEPA new arsenic standards in 2006, drinking water whose arsenic content is between 10 and 50 ppb will need to be treated. To meet the new regulation completely, developing new and cost-effective methods to remove arsenic from groundwater and drinking water becomes imminent. The most commonly used methods to remove arsenic from water involved addition of ferric iron or alumina to induce co-precipitation or arsenic adsorption. Then, the precipitates or colloidal sized particles are separated from water via filtration. In the process of filtration, sand is commonly used due to its inexpensive material cost. The point of zero charge of quartz is 2-3, while that of Fe(OH)3 is 8-9. Thus, under neutral to slightly acidic conditions, iron hydroxide will be sorbed on quartz surfaces. Because of the large particle size of sand grains, their surface area is small. Furthermore, because of its low charge density, quartz has low affinity for ferric iron and iron hydroxide. Therefore, sand will have a low capacity for colloidal ferric iron removal. After filtration, the water may still contain certain amount of Fe, which in turn will cause water coloration and result in rusty tastes. In addition, as the transport of arsenic is positively correlated with the concentration and transport of colloidal iron, a complete arsenic removal may require frequently changes of the filtration media (sand in this case) or use of larger packed filtration columns or beds. Due to the low capacity and affinity of sand for iron, more solid waste may be generated compared to the case when a media with high capacity for iron is used. With several patents granted, using iron/aluminum hydroxide to remove arsenic from water is a proven technology. However, the key issue is the filtration media. Currently, the filtration media used were limited to sand, granular activated carbon, granular activated alumina, but not zeolite.

In this research, the investigators propose to use zeolite as the filtration media to remove arsenic-containing iron/aluminum hydroxide co-precipitates. Their hypothesis is that zeolite has larger surface areas and higher cation exchange and sorption capacity, and the use of zeolite in lieu of sand media to filtrate the arsenic-containing iron/aluminum hydroxide should be cost competitive to that of sand media while the performance will be much better than the sand media. Furthermore, due to an increase in capacity, less system faulting and less solid waste would be produced. In addition to removal of iron/aliminum hydroxide precipitates, zeolite can also remove other undesired metal cations simultaneously. The hypothesis will be tested in batch and column studies aiming to answer the following specific questions:

(1) Is the zeolite able to sorb and retain the dissolved and colloidal Fe(III) that have As sorbed onto it? If so, what is the sorption capacity of Fe(III) by zeolite?

(2) Will the As removal efficiency and capacity be higher than that when sand filter was used?

(3) What would be the overall water quality in addition to As removal? Would the Fe concentration in water be significantly less than that when sand filter was used?

(4) What is the overall cost of the proposed system compared to iron-sand filter system, or iron-granular activated carbon system?

The investigators will conduct batch tests to determine the sorption capacity of Fe3+, Fe(OH)3, a-Fe2O3, a-FeOOH, a-Al(OH)3 and g-AlOOH on sand and on zeolite. The investigators will set up parallel systems in packed column tests to compare the numbers of bed volume to reach an effluent concentration equal to 10% of the input concentration for Fe3+ and other colloidal iron and aluminum hydroxides with sand or zeolite as the filtration media. The investigators anticipate that a significant increase in iron hydroxide or aluminum hydroxide retention by zeolite could be achieved. Thus, the iron/arsenic co-precipitation with zeolite filtration system will have a great potential to evolve into a standalone technology for a community to treat arsenic and iron contaminated water.

Progress/Completion Report, 2009, PDF
Progress/Completion Report, 2011, PDF

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